True or False
Saltwater is denser than freshwater.
True. Dissolved salt adds mass.
What causes water to form droplets on a surface instead of spreading out flat?
Surface tension. It’s a force that pulls water molecules together, making them stick in a tight shape like a droplet.
If an object floats in water, is it more or less dense than water?
Less dense. If it's lighter for its size than water, it will float.
What is refraction?
Refraction is when light bends as it goes from one material to another, like from air to water.
What is the center of gravity?
It’s the point where the weight of an object is balanced in all directions.
A denser object always floats in water.
False. Only less dense objects float; dense ones sink.
What happens to surface tension if you add soap to water?
It gets weaker. Soap breaks the bonds between water molecules, so the surface becomes less "tight."
Why does a rock sink but a piece of wood float?
The rock is denser than water, so it sinks. Wood is less dense, so it floats.
Which travels faster—light in air or light in water?
Light travels faster in air. Water is denser, so light slows down and bends.
Why does a pencil fall over if you try to balance it on its tip?
Its center of gravity is too high and not directly above the tip, so it tips over.
You can balance any object if you find its center of gravity.
True. If you support it at that point, it stays balanced.
Why can small insects like water striders walk on water?
Surface tension holds the water’s surface together like a thin skin. The insect’s legs don’t break that surface, so they can stand or walk.
What is density?
Density is how much "stuff" (mass) is packed into a certain space (volume).
Why does a straw look bent when it’s in a glass of water?
The light bends when it leaves the water and enters the air, making the straw look like it’s in a different spot.
Where is the center of gravity in a perfectly shaped ball?
Right in the center. That’s where its weight is evenly balanced.
Light bends because it changes direction.
False. Light bends because it changes speed when passing through different mediums.
How does temperature affect surface tension?
Warmer water has lower surface tension. The heat makes water molecules move more, so they stick together less tightly.
A boat made of metal floats. How is that possible if metal sinks?
The boat’s shape spreads its weight over a big volume, making the average density less than water, so it floats.
A fish looks closer to the surface than it really is when seen from above water. Why?
Because of refraction. The light from the fish bends as it leaves the water, tricking your eyes into thinking it’s in a different place.
Why do tightrope walkers use a long pole?
The pole lowers and spreads out their center of gravity, helping them stay balanced.
If two liquids of different densities are poured into the same container, the denser liquid will always remain at the bottom regardless of the temperature.
False. While it's generally true that denser liquids tend to stay at the bottom in a layered system, temperature can change this behavior significantly.
Why does cohesion happen in water?
Cohesion, in water, happens because of hydrogen bonds between water molecules.
You place two equal-size cubes in water. One sinks and one floats. What can you say about their densities?
The floating cube is less dense than water, and the sinking one is more dense. Even though they’re the same size, their mass is different.
A mirage on a hot road is caused by light bending because of?
Changes in the air’s temperature and density.
An object with a lower center of gravity is always more stable, no matter its shape.
False. While a lower center of gravity usually increases stability, it’s not the only factor. The shape of the object and the size of its base also matter.